'2(')4 Illinois State Laboratory of Natural History. 



process but that the fifth had two as in all the other species, 

 and in the same year Marsh in his " Cyclopidae and Calanidae 

 of Central Wisconsin" ('93), published the first correct figure 

 of the abdomen, but seems to have been unaware of it, since 

 in his "Cyclopidae and Calanidae of Lake St. Clair" ('95) he 

 says,'' Forbes has recently called attention to the fact that the 

 fourth abdominal segment of the male is without a process 

 and that the fifth bears two processes." His figure in this 

 paper also ('95) is correct. 



The armature of the fifth leg of the female is nowhere 

 represented with exact correctness. The first segment is cor- 

 rectly figured by Forbes ('90) and by de Guerne and Richard 

 in their " Revision," with a spine at the outer apical angle, but 

 this is wanting in Marsh's figure ('95). The second segment 

 is correctly shown in all the illustrations. The third segment, 

 which has three outer spines, three apical ones, and one inner 

 spine, is represented in all the figures without the upper spine 

 on the outer margin. The armature of the spines themselves 

 is nowhere correctly shown, the differences being evident by 

 comparing the specific description with the drawings. 



The left fifth leg of the male is usually represented with the 

 outer apical angle of the first segment unarmed ; de Guerne 

 and Richard, however, figure this correctly. The second seg- 

 ment is often armed with a spine at the outer apical angle, 

 but this is wanting in all of the figures ; nor are the three 

 spines on the outer margin of the third segment shown, there 

 being in most cases only one but sometimes two. The right 

 leg is correct in all the figures. 



The spermatophore is very persistent, and a female is rarely 

 found without one or several. In this species it is a long tube- 

 like sac extending upward and to the left under the abdomen, 

 differing considerably from the same appendage in E. neva- 

 densis, in which it extends downward and backward, and 

 when in position has somewhat the appearance of a keel. It 

 is also much longer in E. lacustris than in E. nevadensis. 



/•.'. lacustris is quite common in the North Central States, 

 being found in the deeper, clearer lakes in connection with 

 Limnocalanus macrurus Sars, Diaptomus sicilis Forbes, 1>. 



